Technical Abstract:
Carbon dioxide flux from soil is a key indicator of soil organic C decomposition, and field estimates of CO2 flux are a critical component in soil C budget calculations. Often cumulative CO2 -C loss from soils are computed from weekly or biweekly measurements; however the consequences of this procedure, specifically with regard to undersampling in time, are generally unknown. This paper examines the temporal variation of soil CO2 flux at several scales. Automated chambers were used to measure CO2 fluxes at hourly intervals to quantify diurnal variations. From these measurements daily and seasonal CO2-C fluxes were calculated. A jackknifing procedure was used to compute the sampling frequency-dependant variabilities associated with the integrated CO2 flux estimates. Our results indicate that failure to account for diurnal variations in CO2-C flux can result in a 20% overestimate in daily CO2 flux if flux estimates are based on a single observation collected between 1100 and 1600 hours. At longer time steps, variance in seasonal CO2 flux estimates increases as time between sampling increases up to 7 days. Strategies are presented for improving interpolation between sampling times to obtain better estimates of cumulative CO2-C loss.